1. Field of the Invention
This invention relates to a method and apparatus for detecting contaminants, and in particular, heavy metal contaminants. More specifically, the present invention relates to a test system wherein a sample is placed in a bottle, the bottle is capped, and crushable reagent capsules are broken, releasing compounds which react with the contaminant and produce a detectable color change specific for the contaminant. The present invention is especially well suited for testing water for the presence of nutrients or contaminants such as lead.
2. Background of the Invention
Contamination of the environment has been increasing steadily for years as the use of metals, chemicals, pesticides, and bacterial organisms has increased. Even though the toxicity of various metals has been known for centuries, it is only recently that there has been a serious increase in interest in minimizing human exposure to such metals. Current public awareness of such pollutants and their associated hazards has created a consumer demand for products that are capable of determining the presence of unwanted and potentially dangerous materials.
Some of the more toxic metals include lead, cadmium, mercury, barium, chromium and beryllium. Lead, in particular, has been subject to much attention due to its presence in articles or paints commonly found in the home. See, for example, "A Simple Direct Estimation of Ultramicroquantities of Lead in Drinking Water Using Sodium Rhodizonate" by E. Jungreis and M. Nechama, Microchemical Journal, vol. 34, pp. 219-221 (1986); U.K. Patent Application No. 2 025 047 A; "A Simplified Method for Detection of Lead Contamination of Soil" by J. Preer and G. Murchison, Jr., Environmental Pollution (Series B), vol. 12, pp. 1-13; and "A Spot Test for Detection of Lead in Paint" by J. Sayre and D. Wilson, J. Pediatrics, vol. 46, pp. 783-785 (1970).
As some of the prior art publications indicate, there is a recognized need in the industry for a simple test or method for determining the presence of lead. However, as will become apparent from the remaining descriptions of the prior art, prior to the present invention, an effective and simple test for lead had not been developed.
In a well known prior art method of detecting lead in paint, sodium sulfide (Na.sub.2 S) is reacted with lead to form lead sulfide (PbS), a black precipitate. The presence of lead is thus confirmed by the appearance of the black precipitate, lead sulfide. This method has several disadvantages: (1) the sodium sulfide is potentially toxic, especially to young children; (2) the black precipitate is difficult to see on dark surfaces; (3) the sodium sulfide releases volatile hydrogen sulfide (H.sub.2 S), which has a noxious odor; and (4) the reagents react with many cations to form black precipitates and thus tend to give false readings on many surfaces.
Another common analytical reagent is a metal complexing agent, rhodizonic acid. For over forty years, rhodizonic acid and salts thereof have been used as analytical reagents to detect heavy metals, including lead, in both qualitative and quantitative analyses. The methodology for using rhodizonate dye is based on two types of tests:
(1) a quantitative determination of heavy metals in solutions using a spectrophotometer to obtain quantitative information; and PA1 (2) qualitative determinations which use filter papers impregnated with the reagent.
In addition, semi-quantitative information can be derived from the use of columns packed with silica gel impregnated with rhodizonate dye. See U.K. Patent Application No. 2 025 047 A.
The Macherey-Nagel Company (Duren, Germany) manufactures a test paper for the determination of lead under the trademark PLUMBTESMO. The PLUMBTESMO strips comprise a heavy filter paper with a reagent impregnated therein. To test for lead in a solution, a strip is dipped into the solution, and observed for a color change that indicates the presence of lead. The PLUMBTESMO strips can also be used to detect lead deposits in motor vehicle tailpipes. However, the PLUMBTESMO strips are not intended to detect lead in a liquid sample.
The instruction sheet that is distributed with the PLUMBTESMO strips indicates that the PLUMBTESMO strips may be used to detect the presence of lead on a degreased surface. However, the instruction sheet impliedly recognizes that the PLUMBTESMO strips are not entirely satisfactory for testing for the presence of lead on a surface. Specifically, the instruction sheet indicates that the PLUMBTESMO strip may have to be held firmly against a test surface for as long as fifteen minutes before an indication of lead develops. Clearly, for nonprofessional, household use, a test strip that must be held firmly for fifteen minutes is entirely unsatisfactory in that many users will become impatient after only a few minutes and will discontinue the application of the PLUMBTESMO strip against the test surface. That type of usage may, of course, result in dangerous false readings, leaving the user with the erroneous impression that lead is not present when in fact lead may be present.
A further disadvantage of the PLUMBTESMO strips is that the test operator must directly handle the test strips, thus being unnecessarily exposed to chemicals. Yet another disadvantage of the PLUMBTESMO strips is that the strips are flat and comparatively stiff, and are thus not readily conformable to curved or otherwise unusually contoured surfaces, such as those that one is likely to encounter on moldings in older houses.
Thus, it should be clear that the lead tests, known prior to the present invention, are not entirely satisfactory. Therefore, there is a need in the art for a test or method for determining the presence of toxic metals, such as lead and cadmium. Furthermore, there is a need in the art for a test for determining the presence of toxic metals in a liquid sample.